var isArray = Array.isArray;

var root = this;

function EventEmitter() {}

if (typeof module !== 'undefined' && module.exports) {
    module.exports.EventEmitter = EventEmitter;
}
else {
    root = window;
    root.EventEmitter = EventEmitter;
}

// By default EventEmitters will print a warning if more than
// 10 listeners are added to it. This is a useful default which
// helps finding memory leaks.
//
// Obviously not all Emitters should be limited to 10. This function allows
// that to be increased. Set to zero for unlimited.
var defaultMaxListeners = 10;
EventEmitter.prototype.setMaxListeners = function (n) {
    if (!this._events) this._events = {};
    this._maxListeners = n;
};


EventEmitter.prototype.emit = function () {
    var type = arguments[0];
    // If there is no 'error' event listener then throw.
    if (type === 'error') {
        if (!this._events || !this._events.error ||
            (isArray(this._events.error) && !this._events.error.length)) {
            if (this.domain) {
                var er = arguments[1];
                er.domain_emitter = this;
                er.domain = this.domain;
                er.domain_thrown = false;
                this.domain.emit('error', er);
                return false;
            }

            if (arguments[1] instanceof Error) {
                throw arguments[1]; // Unhandled 'error' event
            } else {
                throw new Error("Uncaught, unspecified 'error' event.");
            }
            return false;
        }
    }

    if (!this._events) return false;
    var handler = this._events[type];
    if (!handler) return false;

    if (typeof handler == 'function') {
        if (this.domain) {
            this.domain.enter();
        }
        switch (arguments.length) {
            // fast cases
            case 1:
                handler.call(this);
                break;
            case 2:
                handler.call(this, arguments[1]);
                break;
            case 3:
                handler.call(this, arguments[1], arguments[2]);
                break;
            // slower
            default:
                var l = arguments.length;
                var args = new Array(l - 1);
                for (var i = 1; i < l; i++) args[i - 1] = arguments[i];
                handler.apply(this, args);
        }
        if (this.domain) {
            this.domain.exit();
        }
        return true;

    } else if (isArray(handler)) {
        if (this.domain) {
            this.domain.enter();
        }
        var l = arguments.length;
        var args = new Array(l - 1);
        for (var i = 1; i < l; i++) args[i - 1] = arguments[i];

        var listeners = handler.slice();
        for (var i = 0, l = listeners.length; i < l; i++) {
            listeners[i].apply(this, args);
        }
        if (this.domain) {
            this.domain.exit();
        }
        return true;

    } else {
        return false;
    }
};

EventEmitter.prototype.addListener = function (type, listener) {
    if ('function' !== typeof listener) {
        throw new Error('addListener only takes instances of Function');
    }

    if (!this._events) this._events = {};

    // To avoid recursion in the case that type == "newListeners"! Before
    // adding it to the listeners, first emit "newListeners".
    this.emit('newListener', type, typeof listener.listener === 'function' ?
        listener.listener : listener);

    if (!this._events[type]) {
        // Optimize the case of one listener. Don't need the extra array object.
        this._events[type] = listener;
    } else if (isArray(this._events[type])) {

        // If we've already got an array, just append.
        this._events[type].push(listener);

    } else {
        // Adding the second element, need to change to array.
        this._events[type] = [this._events[type], listener];

    }

    // Check for listener leak
    if (isArray(this._events[type]) && !this._events[type].warned) {
        var m;
        if (this._maxListeners !== undefined) {
            m = this._maxListeners;
        } else {
            m = defaultMaxListeners;
        }

        if (m && m > 0 && this._events[type].length > m) {
            this._events[type].warned = true;
            console.error('(node) warning: possible EventEmitter memory ' +
                'leak detected. %d listeners added. ' +
                'Use emitter.setMaxListeners() to increase limit.',
                this._events[type].length);
            console.trace();
        }
    }

    return this;
};

EventEmitter.prototype.on = EventEmitter.prototype.addListener;

EventEmitter.prototype.once = function (type, listener) {
    if ('function' !== typeof listener) {
        throw new Error('.once only takes instances of Function');
    }

    var self = this;

    function g() {
        self.removeListener(type, g);
        listener.apply(this, arguments);
    };

    g.listener = listener;
    self.on(type, g);

    return this;
};

EventEmitter.prototype.removeListener = function (type, listener) {
    if ('function' !== typeof listener) {
        throw new Error('removeListener only takes instances of Function');
    }

    // does not use listeners(), so no side effect of creating _events[type]
    if (!this._events || !this._events[type]) return this;

    var list = this._events[type];

    if (isArray(list)) {
        var position = -1;
        for (var i = 0, length = list.length; i < length; i++) {
            if (list[i] === listener ||
                (list[i].listener && list[i].listener === listener)) {
                position = i;
                break;
            }
        }

        if (position < 0) return this;
        list.splice(position, 1);
    } else if (list === listener ||
        (list.listener && list.listener === listener)) {
        delete this._events[type];
    }

    return this;
};

EventEmitter.prototype.removeAllListeners = function (type) {
    if (arguments.length === 0) {
        this._events = {};
        return this;
    }

    var events = this._events && this._events[type];
    if (!events) return this;

    if (isArray(events)) {
        events.splice(0);
    } else {
        this._events[type] = null;
    }

    return this;
};

EventEmitter.prototype.listeners = function (type) {
    if (!this._events) this._events = {};
    if (!this._events[type]) this._events[type] = [];
    if (!isArray(this._events[type])) {
        this._events[type] = [this._events[type]];
    }
    return this._events[type];
}

module.exports = EventEmitter;